Field of the Invention
The present invention relates to a chair with seat and backrest movable in a synchronized way.
More precisely, the invention relates to a chair in which the seat is movable between a lowered position and a raised position and the backrest is movable between an upright position corresponding to the lowered position of the seat and a backward-inclined position corresponding to the raised position of the seat.
In seats of this type, the resistance opposed by the backrest against the movement of backward inclination is proportional to the weight of the user. Mechanisms of this type are usually known as “weight-activated”.
Description of Prior Art
One of the first “weight-activated” mechanisms is described in the document EP-A-0249584 by the same Applicant, which describes a chair in which the seat is connected to the support structure by means of at least one parallelogram mechanism comprising two rods whose ends are articulated to the seat and to the support structure, so as to allow a movement of the seat between a lowered position and a raised position. The backrest has a support structure which oscillates between an upright position, corresponding to the lowered position of the seat, and a backward-inclined position, corresponding to the raised position of the seat. The support structure of the seat is rigidly connected to one of the rods of the parallelogram mechanism. The parallelogram mechanism is equipped with elastic elements to push the backrest towards its upright position.
The main drawback of chairs equipped with parallelogram mechanisms with articulated rods is the high complexity due to the high number of components.
WO2009/039231 (Herman Miller, Inc.) describes a chair with a deformable seat and backrest, which adapts to the user's weight. This chair comprises two side profiles between which a flexible material is stretched, forming the support surfaces of the seat and the backrest. Each of the two side profiles is formed of an integral element of plastic material with two beam elements connected together by means of integral connecting elements.
This chair structure is specifically dedicated to chairs in which the support surface of the seat and the backrest is formed by a flexible sheet and is not easily adaptable to chairs with different configurations of the seat and backrest.